1. Field of the Invention
The present invention relates to a flat-type cell and a combined battery utilizing the same.
2. Description of the Prior Art
Conventionally, there have been adopted battery cans made of metal as packages of batteries, while adjusting the sizes of cans into shapes of a cylinder, a rectangle and a coin corresponding to the usage. Recently, particularly in the field of portable equipment which is thin and light-weight, there has been a strong demand to attain a thin and light-weigh battery as a power source corresponding to such portable equipment.
Since those batteries adopting battery cans made of metal have a limitation on how thin and light-weight they can be, recent investigation have been conducted to develop batteries adopting packages constituted by thermally sealing a laminated film comprising laminated resin films and metal films, to thereby produce a film armored battery which is remarkably light-weight and thin.
However, at the time of charging and discharging of such a battery, heat is generated from electrode terminals and battery elements due to the presence of the resistance of the electrode terminals and the internal resistance of the battery, thereby causing a possibility of the breakage of the sealed portion by the thus generated heat. Such a breakage of the sealed portion causes a moisture content to intrude into the package to cause a considerable deterioration of the battery performance, thereby leading to lowered reliability.
Various known techniques exist concerning combined batteries constituted of a plurality of film armored batteries. For example, combined batteries disclosed in JP-A-2001-216950 and JP-A-HEI-9-259859 (259859/1997) are mainly directed to use in portable electronic equipment, and are not intended to be used under an increased electric current. Thus, it is difficult to directly divert such combined batteries to unintended usage under an increased electric current.
Meanwhile, it has recently become popular to use film armored batteries for powering electric vehicles and ships requiring larger electric current supplies. In such usage, numerous cells are connected and used as a combined battery so as to attain a higher voltage and a larger capacity, thereby leading to a considerably higher heat generation than a situation for individually using the cells. As such, temperatures of a combined battery have been raised as a whole, in addition to the above-mentioned adverse effects. Excessively raised temperatures may shorten the service life of the battery or damage it. Particularly, in case of a lithium-ion battery such as one adopting an organic solvent as electrolyte and adopting carbon as an active material of negative electrode, it could cause a risk of inflammation to the surroundings when the battery is damaged by unusually higher temperatures.